ON ATMOSPHERIC WAVES. 123 
house observations, and to Rear-Admiral Beaufort, R.N., for the observations made on board 
the surveying vessels.—W. R. B. 
These observations, which were principally undertaken with a view to ob- 
serve the return of the great wave, have been attended with highly interesting 
results. I shall first notice the result of the comparison of the observations at 
this station (Cambridge Heath) with those made at Leicester Square in 1842, 
as fully establishing not only the return of the great wave, but also that of 
other extensive undulations. 
Section I.—Comparison of observations made at Cambridge Heath (north- 
east of London) from Oct. 1, 1845 to Nov. 21, 1845, with observations 
made at Leicester Square from Sept. 14, 1842 to Nov. 25, 1842. 
The observations of 1842 are projected in curves and appended to Sir John 
Herschel’s ‘ Report on Meteorological Reductions,’ 1843. 
1842. I. Plate I. fig. 1 (Report 1843) exhibits an undulation consisting of 
a gentle barometric fall and almost as gentle a rise during seventeen days, 
» namely from Sept. 14 to Oct. 1, interrupted only by the diurnal oscillations, 
which are in general well-developed. 
1845. In 1845 this undulation of seventeen days’ interval returned. It 
was observed from Oct. 1 (the commencement of the observations) to the 
19th, but instead of exhibiting the gentle fall and ascent noticed in 1842, it 
was interrupted by two most remarkable superposed waves. The first oc- 
curred on the 4th, 5th, and 6th of October, and the second from the 11th to 
the 16th. 
_ When these waves (the commencement and termination of each being well- 
marked) are abstracted from the general curve, the resemblance between the 
curves of 1842 and 1845 is very apparent. 
1842. September 14 to October 1. 
1845. October 1 to October 19. 
Il. The curves of the succeeding four days in the two periods 1842 and 
1845 exhibit similar barometric fluctuations, so that the movements during 
the four days succeeding the seventeen-day wave in 1845 are identical with 
those of the four days succeeding the same wave in 1842. 
1842. October Zto 5 . : 
1845. October 19 to tg Lie 
III. The exact identity between the curves of 1842 and 1845 breaks off 
on Oct. 23, 1845. The barometer maintains an elevation above thirty inches 
during the period in 1845 that the movements are not in accordance with 
those of 1842. 
___ IV. Plate I, fig. 3 (Report 1843). The identity between the curves of 
_ 1842 and 1845 again commences on Oct. 27, 1845, and is maintained in a 
_ very close manner until midnight of Nov. 6. 
1842. Ociober 31, midnight to November 11, noon. 
1845. October 27, noon to November 6, midnight. 
Y. In consequence of the movements from Oct. 27 to Nov. 6, 1845, ex- 
_ hibiting so close a similarity to those between Oct. 31 and Nov. 11 in 1842 
_ which immediately preceded the great wave in that year, considerable ex- 
_ pectation was raised that the great wave would set in on the morning of the 
7th. At midnight of the 6th, the similarity between the curves that had been 
so closely maintained during ten days and a half began to fail, and rendered 
it difficult to determine for some days if the preceding movements had really 
_ been followed by the great wave. This question was set at rest as the obser- 
_ Yations proceeded ; for on comparing the curve from the 6th to the 21st with 
_ that of the great wave of Nov. 1842 (Plate II., Report 1843), there was every 
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